Fifteen public water systems in Pennsylvania must stop using a Williston-based water-testing laboratory after investigators found "major violations," according to a news release Tuesday by the Pennsylvania Department of Environmental Protection.

"Analytical Services' laboratory supervisor and laboratory management failed to ensure the accuracy of the analytical data generated and reported" in tests for cryptosporidium, giardia and E.coli in drinking water, the department reported.

Human ingestion of these organisms at concentrated levels can result in severe illnesses.

The lab's analysts "failed to meet the test method requirements for the testing and analysis of microbiology drinking water samples," the release added.

The suspension of service takes place immediately.

Email and phone requests to the laboratory for comment were not returned Tuesday afternoon.

Analytical Services' website states that the company "has helped more than 400 public water suppliers in the United States" meet compliance requirements; and has approval to meet water quality standards in "more than 25 states."

The company is accredited by the National Environmental Laboratory Accreditation Program in New Hampshire, Florida, and Texas; and is a certified laboratory under the U.S. Centers for Disease Control, the website adds.